TDMA communications apparatus

Abstract

If own station detects that a slot S2 previously reserved for own transmission has been occupied by another station when transmitting a message at a current slot S3, the own station sets the occupied slot to a time-out value of zero S0 upon transmitting the message at the current slot S3. At the same time, the own station re-reserves a new slot S5 within an SI in a succeeding frame so that transmission from the own station at the new slot S5 does not conflict with transmission from the other station at the occupied slot, now reserved by other station as slot A.

Description

[0001] 1. Field of the Invention[0002] The present invention relates to a Time Division Multiple Access (TDMA) communications apparatus for carrying out communication using TDMA technology in which a frame is divided into a plurality of time slots, a slot being treated as a unit of data transmission.[0003] 2. Description of the Related Art[0004] In a TDMA communication system, each successive frame is divided into a plurality of time slots based on a common time reference (time base) obtained from the global positioning system (GPS), for example, thereby establishing accurate slot synchronization among a plurality of participating stations (e.g. mobile units such as ships). The participating stations carry out TDMA communication while reserving (allocating) slots for their own transmission of information and messages. In this kind of communication system, such as the Universal Automatic Identification System (UAIS) of which carriage has been required on particular classes of ships s...

AI Technical Summary

Benefits of technology

[0007] A protocol used for slot allocation in autonomous and continuous mode of the UAIS in its stable operating condition is the SOTDMA protocol. The SOTDMA protocol makes it possible to reserve as many free slots as the value of time-out in several frames succeeding to a current frame at the same location as a current slot. (In practice, message 1 is used to realize SOTDMA protocol.)

[0011] The present invention provides an arrangement which enables the own station to resolve this kind of slot allocation conflict by re-reserving another slot in a succeeding frame for own transmission within a predefined period upon detecting that a slot already reserved for own use has been reserved by another station, when transmitting a message of own station. The "predefined period" means a specific period including the slot occupied by the other station and consecutive slots thereof. In the UAIS, this period is referred to as a Selection Interval (SI) which is preset based on the speed, for example, of a mobile unit on which a TDMA communications apparatus of the invention (own station) is installed. Normally, multiple SIs are set in each frame and the own station reserves one slot in each successive SI. Thus, the arrangement of the invention allows each station to avoid transmission conflicts with other stations by re-reserving a new slot in place of any occupied slot beforehand.

[0016] As stated in the foregoing, when the TDMA communications apparatus of the present invention detects that a slot reserved for own transmission in the next frame has been occupied by another station before its slot timing, or when the apparatus detects an occupied slot with sufficient time allowance, the apparatus can re-reserve a replacing free slot within an SI in the next frame by using the SOTDMA protocol. Also, when the TDMA communications apparatus detects that the slot reserved for own transmission within the next SI in the current frame has been reserved by another station before sending own message within the current SI, the apparatus can re-reserve a replacing free slot within the next SI by using the ITDMA protocol instead of ordinary SOTDMA. Since the TDMA communications apparatus can re-reserve a replacing slot, where necessary, it is possible to take action to resolve slot allocation conflicts with other stations caused by a "double-booking" situation as shown above. Furthermore, the TDMA communications apparatus can prevent missing transmissions within SIs involving slot allocation conflicts, and thus a reduction in report rate (message transmission rate), by re-reserving free slots to make up for occupied slots by using the ITDMA protocol in the aforementioned manner even when there is no own slot within each SI due to a "slot pile up" phenomenon which does not mean a "double-booking".

[0018] The TDMA communications apparatus may include a memory for storing violations of individual protocols, such as slot allocation-related violations and transmission-related violations, together with station identifiers (IDs) in the form of violation log. Specifically, in another form of the invention, a TDMA communications apparatus for carrying out communication using TDMA technology in which a frame is divided into a plurality of slots, a slot being treated as a unit of data transmission and the TDMA communications apparatus performing TDMA communication while reserving slots for own transmission, includes a violation information memory for storing violations of individual protocols, such as slot allocation-related violations and transmission-related violations of individual stations, in a manner that allows a comparison between the content of a slot allocation table storing slot allocation status of each station and received messages. Preferably, the aforementioned violations of the protocols include not only obvious violations of UAIS rules but also acts against the spirit underlying the UAIS rules and specifications. The provision of the violation information memory in the TDMA communications apparatus of the invention would make it possible to promote improvements in operation and functional performance of the TDMA communications apparatus installed on a station referring to an off-line report output from the violation information memory.

[0020] Furthermore, the TDMA communications apparatus of the invention serves to reduce the possibility of undesired conflicts since the apparatus can identify causes of individual errors and judge a slot in which an error has occurred due to a total absence of signals as being a free slot which may be reserved for the own station.

Problems solved by technology

One problem in the TDMA communication system is that if any user obviously violates the relevant standards or rules, such as UAIS access protocols, or acts against the spirit underlying the standards and rules, a serious difficulty occurs in the operation of the UAIS, resulting in an inability to ensure efficient and safe navigation of ships.

Should this situation occur and is left unresolved, there will arise a conflict of transmission in the pertinent slot.

Preferably, the aforementioned violations of the protocols include not only obvious violations of UAIS rules but also acts against the spirit underlying the UAIS rules and specifications.

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